//Given a binary tree, find the lowest common ancestor (LCA) of two given nodes 
//in the tree. 
//
// According to the definition of LCA on Wikipedia: “The lowest common ancestor 
//is defined between two nodes p and q as the lowest node in T that has both p 
//and q as descendants (where we allow a node to be a descendant of itself).” 
//
// 
// Example 1: 
//
// 
//Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
//Output: 3
//Explanation: The LCA of nodes 5 and 1 is 3.
// 
//
// Example 2: 
//
// 
//Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
//Output: 5
//Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant 
//of itself according to the LCA definition.
// 
//
// Example 3: 
//
// 
//Input: root = [1,2], p = 1, q = 2
//Output: 1
// 
//
// 
// Constraints: 
//
// 
// The number of nodes in the tree is in the range [2, 10⁵]. 
// -10⁹ <= Node.val <= 10⁹ 
// All Node.val are unique. 
// p != q 
// p and q will exist in the tree. 
// 
// Related Topics Tree Depth-First Search Binary Tree 👍 7468 👎 231


package leetcode.editor.en;

public class _236_LowestCommonAncestorOfABinaryTree {
    public static void main(String[] args) {
        Solution solution = new _236_LowestCommonAncestorOfABinaryTree().new Solution();
        TreeNode t1 = new TreeNode(3);
        TreeNode t2 = new TreeNode(5);
        TreeNode t3 = new TreeNode(1);
        TreeNode t4 = new TreeNode(6);
        TreeNode t9 = new TreeNode(2);
        TreeNode t5 = new TreeNode(7);
        TreeNode t6 = new TreeNode(4);
        TreeNode t7 = new TreeNode(0);
        TreeNode t8 = new TreeNode(8);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t9;
        t9.left = t5;
        t9.right = t6;
        t3.left = t7;
        t3.right = t8;
        TreeNode treeNode = solution.lowestCommonAncestor(t1, t3, t4);
    }
    //leetcode submit region begin(Prohibit modification and deletion)

    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     * int val;
     * TreeNode left;
     * TreeNode right;
     * TreeNode(int x) { val = x; }
     * }
     */
    class Solution {
        public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
            if (root==null || root.val == p.val|| root.val == q.val) {
                return root;
            }
            TreeNode left = lowestCommonAncestor(root.left, p, q);
            TreeNode right = lowestCommonAncestor(root.right, p, q);
            if (left == null){
                return right;
            }

            if (right == null) {
                return left;
            }
            return root;
        }
    }
//leetcode submit region end(Prohibit modification and deletion)

}